This invention is related to additives for coating compositions and in particular to an additive to control the rheology of coating compositions during and after application of the composition to a substrate.
To reduce air pollution, coating manufacturers are using high solids solvent based and water based coating composition. High solids coating compositions contain at least 50% by weight of film forming constituents. However, finishes of these compositions often sag after application and during baking and give a finish having thin spots and an unacceptable appearance. To reduce this sagging, the viscosity of the composition may be increased but this increased viscosity greatly reduces the solids content of the composition which defeats the purpose of a high solids coating composition. An additive is required that will change the rheology of a coating composition so that the composition will be thin at high shear rates (under spraying conditions) but will thicken at low shear rates (after application to a substrate) and will remain thickened during baking of the composition through a wide range of temperatures. The aforementioned description is a phenomenon known as pseudoplastic rheology.
The novel additive of this invention as described hereinafter provides such pseudoplastic rheology to high solids water and solvent based coating compositions.